I have been using Battlefoam products to store all of my miniatures for years now. Specifically their Battletech trays. My problem has been that I don't always know what goes where.
Then there was the time a few years ago I forgot to pack one of my Unseen "Blue-Card" Ralladium miniatures I bought in 1990 after a game at the game store.
So, I started on this project. I made 5mm thick hexes that I superimposed the names of 'Mechs on them, then a band across the top hexside. As you can see below, the band is meant to represent which organization the mech belongs to, and the name. If I can see the name, I know the 'Mech is still missing. I am still in progress with this, I have many more of them to go, however things are moving along. I am hand-painting these, as none of my printers are multi-colored.